Ive been given a gaastra Vapor that has a large tear in the luff sleeve just below the first cam. Would a patch withstand the huge amount of pressure here? It assuming it would be better to sew but is glue an option?

Im pretty positive this sail has a few runs left in it

^^ check the Qld forum. Repairs down at wynnum.

Thanks OlSkool, I might try and get a quote from them but was thinking of just repairing it myself.

Dear Fanatic Youth,
Glue is not an option but hand sewing or machine sewing is an option. For that torn area you can use polyester fabric patch. Good luck.

There is a huge load here , ( that's why it's torn ) . That part inside the luff pocket takes all of the downhaul tension .
Professional repair needed . A good repairer understands these loads and should only do a solid repair . It won't be cheap . I have had a similar repair done and it cost $ 240 .
If the sail is in good condition it , just , may be worth fixing .
A home fix sadly won't work .

... or ... just use it as is.

If it is torn due to high-loading, then whatever it gets fixed with, also needs to handle that strength.
If the sail sets ok, just use it as is.

^^^
Just not further out than you can swim back.
The bottom sail panel will probably rip in half trying to get anywhere near setting . All the load will now be pulling on the luff pocket , ( which should have no tension in this type of cammed sail ) , and the sail panel , ( also not good ) . You will also have to add another 15 cm or so to your extension.
Its going to end ugly .

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mathew said..
... or ... just use it as is.

If it is torn due to high-loading, then whatever it gets fixed with, also needs to handle that strength.
If the sail sets ok, just use it as is.

I have rigged this very sail with old mate (we're good mates) - not enough strength in the luff to set the sail, requires a fair chunk of downhaul tension and just rips the tear further the more you pull...

yep that was my thought too - there's about 200kg pulling on that section......

^^^
Thats a point I'd like to figure out . The amount of pull force on the sail .
Maths heads please join . Decrepit
When I'm rigging a big downhaul cam sail , ( the most effort sail ive ever rigged , NP H2 , 8.7 ) , I'd guess I'd be pulling close to 100 kg.
so.....
If you have three pulleys each end , is it three times my pull or six times , or three times three , or does it double every time it goes over a pulley , possibly OMG 1200 kg ?
So is it 300 , 600 or 900 or even 1200 kg of pull , not counting friction, pulley diameter an stuff ?
Id reakon it's a shipload .
OOHMI GERD I think it's 1200 kg.
Nooooo , can't be.
Trying to do the maths and I'm scaring myself with 3200 kg.
6400 if you double every pulley . That's what the maths says .
Thats two loaded up Land Cruisers .
Help , my brain hurts.

^^ A pulley doubles the force.
So if you pull 100kg on a 6 pulley system. Its 1200kg.
Most of my DH setups only use 5 pulleys

Yes 5 pulleys , not six , base only has 2 ...
That should be 3200 kg.
100 kg ( x 2 pulley 1 ) = 200 xp2 =. 400.xp3 = 800, xp4 = 1600,xp5 =3200
???

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Imax1 said..
Yes 5 pulleys , not six , base only has 2 ...
That should be 3200 kg.
100 kg ( x 2 pulley 1 ) = 200 xp2 =. 400.xp3 = 800, xp4 = 1600,xp5 =3200
???

No, no, no! 1000kg for 100kg pull on 5 pulleys. Each pulley is worth 200kg. Like the Violent Femmes sang , 'Just add em up'.
Theres a pulley calculator thingy on the interweb. Check it out.
Severne Raceboard sail n extension has more pulleys.

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olskool said..
^^ A pulley doubles the force.
So if you pull 100kg on a 6 pulley system. Its 1200kg.
Most of my DH setups only use 5 pulleys

Its been years since I did my rigging cert at TAFE but its not quite as simple as that.

6:1 block is a 6 times loss in rope length not six times the gain in power.

If you like sticking pencils in your eyes here gos.

The Load Formula is


BL = LL + (1 + sum of (sheave x % friction)).

Ok so thats boring and complicated but let me try to break it down!

BL is Becket Load (or over all load on the moving set of pulleys) which is what I assume we are all trying to work out i.e the downhaul force on the sail.

LL Load in the lead rope the - the load on the rope heading to the winch (or the fixed end.)

Friction factor is very important but almost impossible to calculate in our world . There are standard factors for say FSWR (flexible steel wire rope) in an un grooved sheave @ 5% or Natural Fiber in a semi circular sectioned sheave @12% . Our sheaves dont always spin (EG older Gastra stainless ones) or are crusty so very hard to guess a friction factor but Im going to guess its high 17or18%. The friction factor increases on each successive sheave so increases exponentially .

So lets stick to the 100KG LL and a 17% flat FF

so I call it at 100 x (1+ (17x6)) or 100 x (103) or 1030KG.

1030 KG is a lot of tension in a sail.

3200Kg is a massive load as guessed at above would destroy a sail in my opinion.

Its been years since I did my rigging cert at TAFE but its not quite as simple as that.

6:1 block is a 6 times loss in rope length not six times the gain in power.

If you like sticking pencils in your eyes here gos.

The Load Formula is


BL = LL + (1 + sum of (sheave x % friction)).

Ok so thats boring and complicated but let me try to break it down!

BL is Becket Load (or over all load on the moving set of pulleys) which is what I assume we are all trying to work out i.e the downhaul force on the sail.

LL Load in the lead rope the - the load on the rope heading to the winch (or the fixed end.)

Friction factor is very important but almost impossible to calculate in our world . There are standard factors for say FSWR (flexible steel wire rope) in an un grooved sheave @ 5% or Natural Fiber in a semi circular sectioned sheave @12% . Our sheaves dont always spin (EG older Gastra stainless ones) or are crusty so very hard to guess a friction factor but Im going to guess its high 17or18%. The friction factor increases on each successive sheave so increases exponentially .

So lets stick to the 100KG LL and a 17% flat FF

so I call it at 100 x (1+ (17x6)) or 100 x (103) or 1030KG.

1030 KG is a lot of tension in a sail.

3200Kg is a massive load as guessed at above would destroy a sail in my opinion.

^^ wouldnt the friction of each pulley increase the amount of force needed to create the max force at the other end of all the pulleys?

Take the sail to a good sail maker, get them to patch it, colour shouldn't make any difference as its inside the pocket, get them to re-sew luff pocket and hey presto, good cheap sail.

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olskool said..
^^ wouldnt the friction of each pulley increase the amount of force needed to create the max force at the other end of all the pulleys?

(You can tell Im sitting at home with broken vertebrae with too much time on my hands! More pencils stuck in eyes!) Im only following the standard formula. Friction is in fact the most important factor and the only real variable. Im not claiming to be an absolute expert but the friction increases at every pulley as the force does is how I understand it. One thing that really bothers my OCD is the pulleys in parallel as opposed to at 90 degrees. Normally you set up a "Gin Block" where the two sets of pulleys are at right angles to each other in order for the load to be even across the shaft of the pulleys and transfer to the Beckett or load loop, any other way is a big no no. Also the sheaves are supposed to be 12 time the diameter of the rope (in a rope system) so if we use 3mm rope so the pulleys should be 36mm well most are 10mm at best and the Gaastra fitting is 5 or so more of a diversion than a pulley. So I guess sail makers have thrown the rules out the window based on our gear being static as opposed to dynamic, i.e we set and forget until we are de rigging. Out of curiosity I once rigged my NP Ryde only using one pulley at the top and back to the cleat just out of curiosity and was able to set the sail perfectly using a winch so the whole system is in fact redundant in that with enough force applied to the downhaul you can set the sail just fine, some day ill put my load cell on the downhaul and just tied to the center pulley and measure it to see in fact how much force we are applying. Right time to find something else to do ultimately Id advise a professional repair!

The way my brain hurts me is ;
I understand the pulley friction thing , but that only gives me , the puller a problem .
Once the pulling is done and the 100 kg force is applied , ( say for easy maths 80 kg is produced after friction ) , isnt it then a matter of doubling over each pulley ? Because you are doubling the rope length .
5 pulleys ,, 80kg turns to 160 over first pully , 320 , 640 , 1280 , 2560 kg ?

en.wikipedia.org/wiki/Block_and_tackle#Mechanical_advantage

Someone should do a "how much can we pull" before we assume 100Kg of force.

Peterowensbabs, holy cow thats a lot more science than id ever dreamed of. Technical stuff. Guess we all take it for granted. Thread the rope yank on it n away we sail.

The mechanical advantage of downhaul pulley setup is 8:1 or 6:1. If you apply a force of 100 kg it translates into 800 kg of downhaul on the sail for 8:1, or 600 kg for 6:1. Someone should be able to pull approx their body weight on the downhaul rope.

www.canyoneeringusa.com/techtips/test-report-hard-can-pull

www.unifiber.net/en/windsurfmast-extensions

My Overdrive M2 is 8 to 1 and I guess by how much the rope cuts into my hand I'm not pulling more than 50kg
interesting is that the first 2 pulleys you go through on the sail are plastic and the second 2 are metal. What would be really nice is if the pulleys had bearings in them, probably wouldn't like sea water much though.

Hi Fanatic Youth. I often repair my own sails by hand stitching. Ive done a blown out luff on a 11m sail from an exploded mast on a hot day. Ive also done a number of blown out lower panels from crashes and a ripped off head cap from material rot, or sometimes people just giving a sail away as its not worth the cost of the repair. My hand sewing never looks very good so don't expect to sell the sail, but its all stood the test of time. Ive found using a regular needle to be useless in most cases other than stuff like board bags. The key is to use a sewing machine needle, which you may need to hold with pliers for strength. You pass the tip through the material, then loop a bottom thread through a coil of thread and then pull the needle back. It locks to the bottom thread. Set up the bottom thread with your first pass through the material. The stitch doesn't slide like hand stitching and pressures the fabric together. BUT its tedious slow work to pass the thread through the loop, but it is worth it.
The next key for me is to use braided fishing line as your thread. It holds a knot, and is incredibly strong, and cheap from department stores.

The advantage is you don't need to pull the sail to pieces to pass it through a machine. The disadvantage is it takes ages, but if you have the time you can do it.

If you need to stitch mono to Dacron put sail sticky-back along both sides of the mono and you can use this method to stitch that. My normal hand sewing would be far too loose and mobile for this but the sewing machine needle hand sewing really presses the fabric together well.

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FanaticYouth said..
Ive been given a gaastra Vapor that has a large tear in the luff sleeve just below the first cam. Would a patch withstand the huge amount of pressure here? It assuming it would be better to sew but is glue an option?

Im pretty positive this sail has a few runs left in it

Further to my above comments on sewing machine needle hand stitching, this repair is obviously a critical one. Id be tempted to find some material like tie downstraps or similar and try to distribute the load a fair way above and below on both sides. I think your sail material is degraded and will just tear again unless you reall distibute the load.

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Heavy1 said..
Hi Fanatic Youth. I often repair my own sails by hand stitching. Ive done a blown out luff on a 11m sail from an exploded mast on a hot day. Ive also done a number of blown out lower panels from crashes and a ripped off head cap from material rot, or sometimes people just giving a sail away as its not worth the cost of the repair. My hand sewing never looks very good so don't expect to sell the sail, but its all stood the test of time. Ive found using a regular needle to be useless in most cases other than stuff like board bags. The key is to use a sewing machine needle, which you may need to hold with pliers for strength. You pass the tip through the material, then loop a bottom thread through a coil of thread and then pull the needle back. It locks to the bottom thread. Set up the bottom thread with your first pass through the material. The stitch doesn't slide like hand stitching and pressures the fabric together. BUT its tedious slow work to pass the thread through the loop, but it is worth it.
The next key for me is to use braided fishing line as your thread. It holds a knot, and is incredibly strong, and cheap from department stores.

The advantage is you don't need to pull the sail to pieces to pass it through a machine. The disadvantage is it takes ages, but if you have the time you can do it.

If you need to stitch mono to Dacron put sail sticky-back along both sides of the mono and you can use this method to stitch that. My normal hand sewing would be far too loose and mobile for this but the sewing machine needle hand sewing really presses the fabric together well.

Thanks Heavy that's really helpful, i've got sewing machine needles and fishing line so i think that will be the best option. Would sewing tiedownstrap material reinforcements lengthways over the top of a monofilm or dacron patch work? (Doesnt need to look pretty just has to hold). Also do you have any advice for getting holes through mutliple layers of thick material for the thread?

Cheers Harry

Be sure its braided fishing line. May have to hold needle with pliers.

can't be specific about your repair, but you need to put sticky back on both sides of mono if you have to stitch it. Can you stitch up the edge along a seam?